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Thing is cyril, a voltmeter may not give an accurate reading as it will be pulsing, er then again, I suppose it HAS to be either 12V or 5V and maybe if its going at a fair old rate then the meter may well read a decent average, my card only has a 2 pin fan, but my board has a few 3 pin ones, If I get chance I'll get me scope out the loft an have a measure.

This sig In memory of my kid sister, Mandy. Died 14-8-02 aged 30.
Murdered for nothing at all by Louise Berry

I think you are spot on with your last detailed description, It's just my understanding of it that was awry. I'm beginning to grasp it now.

I have checked the plug which was not easy considering how tiny it is. I cut up an old HDD jumper to make some female pins. (standard mobo 3pin plug shown in the pic for size).

The plug:-

Pin 1. red = +12v

Pin 2. rotation = +5.1v

Pin 3. Black = ground (-12v)

I then tried using another fan, (an Intel P3 retail), that has rotation detection. I powered it via a PSU 4 pin plug and connected the output rotation to the #2 pin on the Asus GF3 header (no other pin on the Asus card was connected). This worked showing fan speed in Smart Doctor, (all be it lower due to the slower rpm of the P3 fan).

I then removed this P3 fan and connected the multimeter to the #3 pin (ground) and the #2 pin rotation. Set the meter to ohms and used an air blow gun to spin the fan blades. (it had no power going to it at this time). This reported a varying meter reading related to fan speed.

So it looks as if it has the pull up resistor and is being supplied by the fan with a " Ground - NC - Ground - NC" etc... at a pulse speed dependent on fan revs.

It looks as if the 555 will do but I think I'll still need more help with the circuit layout/diagram to be able to buy the correct components and build It.

I sent you an updated diagram of the Timer cct by e-mail. I am afraid I have no idea how to attach it here.
I am not sure if your e-mail provider will accept it since it is 5 Megs.
Maybe you can clue me in on how to attach pictures to a BBS. You obviously have a good handle on it.
Great pictures by the way. I am afraid to ask how much that Nikon cost.

Sorry about that. That is what my scanner saved it as. I did not have much time to change it as my wife and son were both bugging me to get off the computer. Yes I would appreciate the program and I do believe I have some webspace but I have never used it.
If the program is too big to send me, a url where I could download it would be appreciated. Would that same thing work with soundfiles?

Getting back to the diagram. When I tested the circuit it gave a steady 100hz output which should give you an RPM indication of 6000. It would however depend on the tolerance of the components you bought. Could be a few hundred RPM either way. Yes 5V is to power the 555 timer. In the original diagram it said you could use 5-15V but I tested 12V and the Frequency was unstable. Sounded like an airplane taking off. The frequency started at 100hz but kept increasing until it reached about 800hz.(48000RPM)

Since you have 5V available in your case however this should not be a big problem. It just would have been easier with 12V since you could have used the connector off the fan and just plugged the circuit board in. No extra connections.
Do you not have someone there who can make this for you?
By the way once you have it built you can test it by putting a speaker across where the RL was in the original diagram(between the 5v wire and the o/p wire). You should here a low frequency hum coming from the speaker if the cct is working.

Having a look at your schematic for the 555, and it is slightly different than the form I am used to using.

Here is a slightly different schematic for an astable multivibrator using the 555, modified from page 7 of the datasheet:
The only difference is the secondary capacitor. The other schematic has a large capacitor bridged over the voltage source, while this one has a smaller capacitor connected to the control-voltage pin of the 555.

I have used this orientation many times, and from a quick test, it seems to be stable at ~100Hz from &lt;5v to &gt;16v

If, as it seems, you need to reproduce an OC-GND oscillation, the easiest way would be to pass the output of the 555 through a ~10k resistor and into the base of an NPN transistor. Then have the collector connected to the SIG and the emitter connected to GND. This will provide the required OC-GND signal on the fan header.

PS.
sorry about the crappy ASCII schematic. I didn't realise UBB chops out all the extra spaces. Anyway... that circuit does work and is elegant in its simplicity, but the 555 approach is probably the better choice.

------------------
"Duct tape is like the Force. It has a light side, a dark side, and it
holds the universe together...."
* Carl Zwanzig

"Duct tape is like the Force. It has a light side, a dark side, and it holds the universe together...."
* Carl Zwanzig

Thats great Bartleby. I would go with that if it is stable at 12V since you could use your fan connection only. Let me know if you have any questions or you just want me to confirm the stability. I do not doubt it though. It was probably that big value capacitor at the output that was the problem.

Now I have a question for you. I must have been dopey the other night and clicked the wrong button at a website. Now I have a 266mhz thunderbird (1.1G) coming instead of a 200mhz. I have the kt133 chipset and not the kt133A. Am I correct in assuming this will still work just at 200mhz or am I going to have to send it back when it comes?

I think your 266mhz CPU will work ok but you wont get it to boot at it's default 133mhz fsb out of the KT7 chipset. It would be default set at, (8.5x133 I guess), although that gives 1130mhz? to run it you'd first have to unlock it and run 11 x 100. You maybe able to get the fsb up a bit, (10 x 110), like you are running with the Duron. but not much more with a kt133 chipset KT7.

Yes I know about the pencil trick but I would use silver conductive epoxy, not the pen but the stuff you have to mix. That way you only have to do it once. That is what I used to unlock the duron. Worked great.

Saw some conductive tape on one site, already spaced and everything. Looked like the real rig for someone with little experience and no microscope. It wasn't cheap though. Think I will stick with the epoxy. I get it for free at work anyway.
Good luck with the project. Keep us informed.

As long as the 266 will run on this machine and not in a degraded mode from what the 200 would have run then I will keep it. If I change boards later it may come in handy anyway. I want to play with the duron some more to see if I can hit a gig first. Do you think I can do this with just better cooling. I use a socket-AHO with chemtronics HS compound. The heatsink is not lapped. When I tried for a gig both ways it posted but I got windows protection errors. That makes me think the voltage needs to be increased but I would have to mod the board for that and I would prefer not to.